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How Toxic is Your Sunscreen?
Dr Peter Dingle presents the evidence behind a growing concern about chemicals in sunscreens.
During the past 50 years, we have increased the number of synthetic sunscreen chemicals that we use. We have done this with virtually no consideration of how vulnerable we are to these chemicals - or how little we know about their subtle and cumulative toxic effects. We assume that because they are so easily purchased from the supermarket shelf, they must be safe to use. Wrong! Many of these chemicals are known to be toxic; very few are carefully studied before they are put on the shelf and made available to the general public. In fact, many of these chemicals have been used for more than five decades without any deliberation about their potential toxic effects. There is no doubt that the products in everyday sunscreens are toxic. The only real question is: what effects do they have on you and your family?
The question of whether sunscreen prevents skin cancer remains unanswered. More than a dozen epidemiological studies show an increased risk of skin cancer to the sunscreen user. A review of studies on skin cancer and sunscreens by "Science News" found that people who used sunscreen were more likely to develop basal cell cancer than people who did not. The possibility remains that these products may be contributing to skin cancers. This is supported by the fact that the toxic chemicals used in sunscreens could very well constitute a potential mechanism for the development of skin cancers.
Many of the chemicals in sunscreens have minimal toxicological effects when first applied to the skin. However, once exposed to sunlight, reactions occur between the sunscreen's active and inactive ingredients and the epidermis. Toxic reactions include inflammation, dermalogical effects, allergic reactions and photogenotoxic (DNA altering) effects. Many chemicals in sunscreens have been found to be phototoxic (becoming toxic when exposed to light), causing burning, irritations, pigment changes and photoallergic effects such as hypersensitivity to chemicals.
Titanium dioxide, or Ti02, has been found to form harmful free radicals that react with skin cells, resulting in intracellular damage, including damage to DNA. On absorption of UV light, photo-generated titanium dioxide particles create singlet oxygen, superoxide anions (O2-) and hydroxyl radicals (OH-) that are potent free radicals. This damage can lead to the development of mutant cells and skin cancers.
Octyl methoxycinnamate (OMC) is one of the most frequently used chemical UV filters worldwide and has been reported to cause photosensitisation and photoallergic effects. OMC easily penetrates the upper layer of the skin and, when exposed to UV radiation, generates free radicals in skin cells. Recent studies indicate that OMC may also have significant undesirable effects as a xenoestrogen.
Extensive research has shown that a number of UV filters frequently used in the formulation of commercial sunscreens, such as 4 MBC, octyl methoxycinnamate, oxybenzone (benzophenone-3), octyl-dimethyl-PABA and octinoxate, possess endocrine activity. Endocrine disruptors are chemicals that interfere with endogenous hormone action and/or production. These have been implicated in the development of a number of diseases in both males and females, including cancer of the mammary glands and reproductive organs, as well as the abnormal development of the male reproductive system. In one study, the application of three active ingredients commonly found in sunscreens (oxybenzone, 4-MBC and octinoxate) for one week led to a drop in testosterone and estradiol levels in men. More worrying is that these chemicals have been found in breast milk at concentrations known to have oestrogenic effects.
4-Methylbenzylidene camphor (4-MBC) competes with estradiol for oestrogen binding sites in the uterus, indicating that it may act as an environmental oestrogen. Laboratory tests on rats exposed to 4-MBC revealed that male rats born to mothers exposed to this compound had lower testis weight, experienced delayed puberty and decreased adult prostate weight. Human trials found that both OMC and 4-MBC were readily absorbed through the skin and were detectable in urine.
These compounds may pose an even higher danger to prepubescent children with low levels of endogenous hormones. Youngsters are likely to be exposed to greater concentrations of these compounds as a result of their larger surface area to volume ratio, undeveloped toxin elimination systems, greater application rates and the fact that they are likely to swallow small amounts when the sunscreen is being applied to their face and lips.
Daily use of a sunscreen with benzophenones can cause photo-contact dermatitis, rosacea, burning, itching and erythema. Benzophenone, along with menadione, form free radicals which can initiate a chain reaction that will cause damage to anything it comes in contact with, including cell DNA.
Oxybenzone (benzophenone 3) is a benzophenone derivate commonly used which is rapidly oxidised to become a potent free radical and linked with cell damage. It has also been linked with allergies and xenoestrogenic properties. A recent study found that mothers with high levels of oxybenzone in their bodies were more likely to give birth to underweight baby girls which is linked with many health complications later in life. In the words of the researcher, "It would be prudent not to apply oxybenzone to large surface areas of skin for extended and repeated periods of time, unless no alternative protection is available."
A study by the Center for Disease Control in the US found that 97 per cent of the 2,500 people tested aged six years and up had oxybenzone in their urine. An earlier study found oxybenzone in the urine of all adults tested and being excreted many days after the last application, which suggests a tendency to accumulate in fatty tissues in the body.
Avobenzone is another compound that upon exposure to UV light generates free radicals; PABA (para-aminobenzoic acid) was one of the first commercially used UVB sunscreens. The US Food and Drug Administration limits PABA content in sunscreen to a maximum of 15 per cent of total ingredients; in Europe, the limit is set at 5 per cent. PABA is listed as a permitted active ingredient (of concentration up to 15 per cent) in Australia under the TGA (1989). PABA is prohibited as a sunscreen ingredient in countries such as Canada due to its ability to affect DNA in human cells in a manner that results in increased susceptibility in some people to skin cancer. PABA has been found to form potent free radicals when exposed to UV light.
Padimate A, an ester of PABA, (amyl para-dimethylaminobenzoate) causes phototoxic reactions. Padimate A reacts with UVA to produce symptoms widely resembling sunburn in some individuals without sunburn cells.
Padimate O (2-ethylhexyl-4-dimethylaminobenzoate ), when exposed to sunlight, generates free radicals that cause strand breaks on DNA. An experiment with Padimate O found that it produces singlet oxygen (free radicals) upon illumination and increased indirect DNA damage by a factor of 75 over sunlight exposure alone.
In 1994, researchers at the Harvard Medical School found that the ingredient psolaren in sunscreens is an extremely efficient carcinogen. People with psoriasis are at greater risk than others, as their squamous cell carcinoma rate was found to be 83 times higher than that of the general population. PBSA (2-phenylbenzimidazole-5-sulfonic acid) and Parsol 1789 are also linked with causing DNA damage.
Octyl salicylate and Dibenzoylmethanes are associated with an increase in photoallergy and contact allergy, as well as the other dibenzoylmethane derivatives such as 5-methoxypsolaren (5-MOP) and isopropyl dibenzoyl methane (Eusolex 8020).
Preservatives can be just as toxic as the sunscreens. Formaldehyde, a chemical that causes cancer in some animals and a strong skin irritant, is also used by some manufacturers as a preservative. DMDM Hydantion, diazolindinyl urea (also with a trade name GERMALL) and quaternium are chemicals that release formaldehyde and have been associated with skin senitisation and rash.
Excipients make up approximately 80 per cent of sunscreens and act as the carriers or base materials of a product. They "receive" and carry the other ingredients. Excipients include mineral oil, petrolatum, isopropyl esters, lanolin derivatives, aliphatic alcohols, emulsifiers, fragrances, thickeners and preservatives. In Australia, sunscreen manufacturers only have to list the "active ingredients," those that are used in blocking the sun, and preservatives. By contrast, cosmetics legislation makes companies list all the ingredients, despite the fact that sunscreens may be applied all over the body, multiple times each day and all over our kids.
Most of the major active ingredients in sunscreens that have been tested for their ability to enter the blood through the skin have shown positive results. One experiment found benzophenone-3, octyl-methoxycinnamate (OMC) and 3-(4-methylbenzylidene) camphor (4-MBC) were all detected in plasma one to two hours after one application. Peak median plasma levels were reported at three to four hours after initial application and participants continued to excrete it many days after the last application of the chemical, which suggests it may accumulate in fatty tissues in the body.
A large proportion of the active ingredients in sunscreens can also act as penetration enhancers that speed up the movement of other chemicals through the skin and into the blood. In a number of studies, sunscreens have enhanced the penetration through the skin of pesticides such as 2,4 dichlorophenoxyacetic acid (2,4, D), paraquat, parathion and malathion and industrial solvents.
Safer barriers
A number of products are now available that afford just as good sun protection as the synthetic toxic sunscreen ingredients, but with a much reduced risk. Black and green tea extract gel was found to first prevent erythema and acute sunburn because of direct sunlight, as well as to repair DNA damage inside the skin. Human skin is capable of absorbing various nutrients directly and clinical studies have indicated that tea polyphenols are readily absorbed when topical applications are applied to the skin. Formulations containing products such as vitamin A, vitamin E, lycopene and green tea are at present readily available on the cosmetic market.
Zinc oxide is considered considerably safer than titanium dioxide and covers the full UVA and UVB spectrum from 290 to 400nm, the most complete spectrum. Microfine zinc oxide is less white than titanium dioxide as a sunscreen ingredient and it is more protective against long wave UVA.
Buy only products that list all the ingredients. The product packaging must state as such: all ingredients are listed. You don't want them to just accidently miss one. The list will be at least 10 items long and in most cases much longer. The claim of being "natural" can be very misleading. Even more misleading, the term "natural" can be a part of the name of a product and therefore not necessarily a claim! Perhaps a better approach is to ask for products that are free from synthetic chemicals. Claims of being chemical-free usually imply this but are not really precise enough. Everything is made from chemicals, so "chemical-free" is not possible. Organic products refer to products that have an extremely high level of certification and quality assurance. This means a lot of work has already been done to validate their safety. None of the toxic ingredients I have listed as toxic above are permitted in organic certification. To find the safest sunscreens, look for products that resemble food ingredients. This would include a plant-based oil, green tea and vitamin E. In the future, all sunscreens will be made of edible ingredients probably with a little zinc oxide thrown in.
A final word
Only through consumer pressure will the bigger companies change to safer, less toxic ingredients in sunscreens. Science has never been enough to change the world - it can only help individuals make better choices and they can then change the world.
My aim is not to drive people out into the midday sun without protection. My goal is to get people to think twice about the products they use.
Good luck and good health to you and your family.
The complete study (50+ pages) is available at www.drdingle.com
Peter Dingle is Associate Professor in Health and the Environment at Murdoch University, Western Australia
http://www.novamagazine.com.au/a ... _toxicsunscreen.htm |
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我的揾工经验 (2006-3-30) StKilda 
回到过去（S篇）— SK IMAGE (2010-7-12) Pluggedboy 
楼主:viviancn
发表于 2011-11-12 21:56
发表于 2011-11-12 23:07
